I deal with dry eyes, but mine are due to Thyroid eye disease.
I have Hashi's and Sjogren's and mixed connective tissue disease. As to the dry eyes, I'd bet on the Sjogren's. Mine started off with dry mouth and throat (really, really dry). I was diagnosed with MCTD first, then Hashi's and the Sjogren's was the last. Many of the symptoms of the various auto-immune diseases are the same, so it is difficult to pinpoint which disease caused which symptoms, the main thing is to get them under control. And once you have one, it seems like a domino thing, you just keep getting more.
Yes, I agree....that is a tough call. I would focus on treating the dry eye symptoms and not focus on why, for now. It is a tough catch 22 for a lot of us.